In remote meter reading systems, such as wireless metering applications, wireless utility meters are read without visual inspection or physical access to the meters. Wireless utility meters intended for use on wireless networks are required to undergo a certification process before they are granted carrier approval for network access.
Traditionally, wireless networks had certification requirements that included signaling behavior verification, which is the control protocol between the network infrastructure and the end user device. Also, network interaction was verified during both steady-state and transient conditions. However, these measurements did not characterize the over the air, radio frequency performance of communication systems. They did not convey the communication systems' sensitivity (its ability to receive low signals), that is, they did not determine how small a signal the communication systems could “hear” or receive. Further, the certification measurements did not characterize the total radiated power from the communication systems during transmission. Consequently, communication systems experienced connectivity and retransmission problems because of inadequately characterized radio frequency product performance. Unreliable connectivity, dropped calls, and data retransmission problems adversely affected the quality of service. As a result, wireless carriers shifted their focus to improving system performance and ensuring that communication systems, operating on their networks, met new over-the-air, system level requirements.
In response to increasing demand to improve wireless device performance, the United States based Cellular Telecommunications & Internet Association (CTIA) adopted more stringent, system level certification requirements that included total isotropic sensitivity (TIS) and total radiated power (TRP). The total isotropic sensitivity and total radiated power measurements reflect a system's performance in an idealized anechoic and shielded radio frequency environment.
Further, the Cellular Telecommunications & Internet Association (CTIA) require communication systems to meet specified values for TIS and TRP, expressed in dBm, for each frequency band that is supported by the product. More specifically, communication systems operating in the 850 MHz band are required to meet an absolute, quantitative value of −99 dBm for the total isotropic sensitivity. Additionally, communication systems operating in the 1900 MHz band are required to meet a quantitative value of −101.5 dBm for the total isotropic sensitivity. Similarly, the total radiated power value is 22 dBm for communication systems operating in the 850 MHz band and is 24.5 dBm for communication systems operating in the 1900 MHz band. Communication systems which do not conform to these new performance requirements are not certified or granted access to the wireless carrier's network.
Utility meters, such as wireless electricity meters, that access public wireless networks are an example of this communication system. Wireless electricity meters that used previous antenna designs failed to pass these new and stringent certification requirements. As a result, previous antenna designs failed the wireless product certification process that was, and still is, required by the Cellular Telecommunications & Internet Association.
One previous antenna design embedded the antenna inside the wireless electricity meter. The antenna was embedded within the communications circuit board, located inside of a dielectric housing under the meter cover, wherein the antenna conformed to the internal surface of the dielectric housing. Such designs degraded the over-the-air, system performance by introducing unintentional sources of interference such as noise coupling and signal reflection.
Other designs positioned the antenna outside of the meter cover. This design often draws unwanted attention to the external antenna. An external antenna positioned outside of the meter cover introduces installation and maintenance problems for the customer. Other issues include destruction of the antenna by the weather, people, or other circumstances. In addition, gains (dBm) of an external antenna are reduced due to coax cable losses that exist between the external antenna and the wireless modem device located within the wireless electricity meter. Moreover, the antenna's system level performance is adversely impacted by the presence of radiated noise emitted from electronic components and metal structures within the meter. Consequently, the uniformity of the antenna's transmit and receive patterns, the values of the total radiated power, and the values of the total isotropic sensitivity are adversely impacted.
For these and other reasons, there is a need for a system that addresses over-the-air, system level performance of wireless utility meters.